Exclude all subcategories in the_category (post)

There is no filter for the_category. All that the_category does is to echo get_the_category_list. Have a look at the function in wp-includes/category-template.php lines 273 – 275

273 function the_category( $separator="", $parents="", $post_id = false ) {
274         echo get_the_category_list( $separator, $parents, $post_id );
275 }

Personally I would say that the_category is incorrect for what you want to do, as you don’t need to display any type of parent/child relationship

You can take a look at wp_list_categories which gives you a lot of flexibility. wp_list_categories is also not just limited to categories, is can be used for custom taxonomies as well.

The parameter that you should have a look at here is depth which you can set to

0 – All Categories and child Categories (Default).
1 – All Categories displayed in flat (no indent) form (overrides hierarchical).
1 – Show only top level Categories
n – Value of n (some number) specifies the depth (or level) to descend in displaying Categories

Here is a slightly modified version of the code found in the codex page. I’ve set the depth parameter to 1, which will only show the top most category level

<?php 
$taxonomy = 'category';

// get the term IDs assigned to post.
$post_terms = wp_get_object_terms( $post->ID, $taxonomy, array( 'fields' => 'ids' ) );
// separator between links
$separator=", ";

if ( !empty( $post_terms ) && !is_wp_error( $post_terms ) ) {

    $term_ids = implode( ',' , $post_terms );
    $terms = wp_list_categories( 'title_li=&style=none&echo=0&depth=1&taxonomy=' . $taxonomy . '&include=" . $term_ids );
    $terms = rtrim( trim( str_replace( "<br />',  $separator, $terms ) ), $separator );

    // display post categories
    echo  $terms;
}
?>

Related Posts: